The present invention relates to a method of manufacturing a radial tire having a belt (breaker) and a band wound thereon, more particularly to a method of forming a tread ring separately from a tire main body, and also relates to a tread ring forming apparatus.
In general, high speed radial tires for passenger cars, sport cars and the like are provided with a belt (breaker). As the belt cord angle is relatively large with respect to the circumferential direction, the hoop effect is less and the belt is liable to be lifted by high speed rotation. Thus, a band whose cord angle is substantially zero is further wound on the belt to provide a tight hoop effect.
On the other hand, the tire tread is usually provided with a camber. Therefore, it is preferable that the belt is also provided with a similar camber.
Such a belt camber can be obtained by a profiled belt drum of which profile is a convex line in a cross section including the drum axis and also a convex line in a cross section normal to the drum axis. Namely, the drum has a three-dimensional curvature. Such a drum is disclosed in Japanese patent publication Nos. JP-B2-5-44914 and JP-B2-6-51368.
In practice, however, due to high cost, it is difficult to prepare or make such a profiled belt drum for various tire sizes. Further, it is almost impossible to exactly adjust or control the three-dimensional curvature according to the output.
Therefore, sometimes the belt camber is decreased to almost zero, though the tread camber is maintained. As a result, in the vulcanizing mold, the tread rubber is liable to be moved and compressed unevenly especially in the tire shoulder portion to disturb the uniformity of the tire.
Further, the radially inward compressive force that the belt and band receive from the inside of the mold is relatively large in the belt edge portions than the center due to the curvature corresponding to the tread camber. As a result, the band tension decreases in the tire shoulder and the high speed durability decreases.
Therefore, a primary object of the present invention is to provide a radial tire having a belt and band whose dimensions are accurately controlled to improve the tire uniformity and the like.
Another object of the present invention is to provide a method of manufacturing such a radial tire by the use of a belt drum comprising novel segments.
Still another object of the present invention is to provide a tread ring forming apparatus including the belt drum.
Still more another object of the present invention is to provide a method of forming a tread ring by the use of the tread ring forming apparatus.
According to one aspect of the present invention, a method of manufacturing a radial tire comprises a process of making a tread ring by the use of a belt drum,
the process of making a tread ring comprising the steps of
forming a raw belt by winding a strip of rubberized high modulus cords on the belt shaping face,
forming a raw band by winding at least one organic fiber cord on the radially outside of the raw belt at an angle of 0 to 5 degrees to the circumferential direction of the drum, and
forming a raw tread portion by applying a strip of raw tread rubber on the radially outside of the assembly of the raw belt and raw band.
The radial tire comprising a carcass extending between bead portions, a belt disposed radially outside the carcass, the belt having a belt camber (A) of 2 to 4% of the section width of the tire and an outside diameter (2Rc) at the tire equator, and a band disposed radially outside the belt and inside a tread rubber.
The belt drum comprises segments arranged around the axis of the belt drum, the segments being movable radially between a radially inner position and a radially outer position, each segment having a radially outer surface, the radially outer surfaces of the segments in the radially outer position collectively forming a belt shaping face for supporting the radially inside of a belt material wound thereon.
In the tread ring, the inside circumference Bc of the raw band at the tire equator is
2Rcxc3x97xcfx80xc3x97a 
and the inside circumference Be of the raw band 7 at the axial edges of the raw belt is
2(Rcxe2x88x92A)xc3x97xcfx80xc3x97axc3x97b 
where
0.94xe2x89xa6axe2x89xa60.99, 
0.97xe2x89xa6b less than 1.0.